Calcium carbonate deposition on cellulose

Cellulose powder was found to be a substrate favoring the deposition of cal cite crystals from stable supersaturated solutions at pH 8.50 and at 25 deg rees C, Kinetic analysis of the initial rates showed that they were proport ional with the relative supersaturation with respect to calcite. Analysis o f the dependence of the induction periods on the initial solution condition s showed that the number of ions forming the critical nucleus was 5. The se cond-order dependence of the rate of precipitation of calcite on cellulose on the solution supersaturation suggested a surface controlled mechanism. T he surface energy of the calcite nuclei growing on cellulose was calculated to be 46 mJ m(-2) from the dependence of the induction time on the solutio n supersaturation, The overgrowth of calcite on cellulose was done selectiv ely on the macromolecules possibly through active sites formation at ioniza ble functional groups (-OH), The nucleating capability of cellulose was fou nd to be comparable with that of sulfonated polystyrene and significantly l ower in comparison with sulfonated polystyrene divinyl benzene copolymer on which vaterite was formed. This fact together with the selective growth of the most stable calcite suggested that stereochemical factors are very imp ortant in determining both the kinetics and the nature of the polymorph for med. (C) 2000 Academic Press.